The present invention relates to a protolytically leaving group-containing copolymer and a process for its production.
A protolytically leaving group-containing copolymer has a group which is eliminated by proton and replaced with hydrogen atom and, upon the replacement of such groups with hydrogen atoms, the copolymer undergoes changes in the characteristics such as solubility in alkaline aqueous solution and so forth. When such a copolymer is caused to coexist with an acid catalyst acting as a proton donor and the system is exposed to light, plasma or radiation or heated to generate a proton from the acid catalyst, the characteristics such as the solubility in alkaline aqueous solution is significantly changed before and after irradiation. By taking advantage of this property, the copolymer can be applied for various purposes in chemical industry, for example photolithographic materials and low profile additives.
Japanese Kokai Publication Hei-11-171836 discloses a polymer having a repeating unit composed of a certain allyl ether derivative. This polymer has one protolytically leaving group as a defined functional group in the repeating unit, by virtue of which it can be utilized as a photolithographic material or a low profile additive. However, the polymer has room for structural sophistication to further improve the characteristics such as solubility in alkaline aqueous solution in the presence of a proton.
Japanese Kokai Publication Hei-9-244246 discloses a radiation-sensitive resin composition comprising two kinds of copolymers each having two kinds of repeating units of defined structures in combination, and Japanese Kokai Publication Hei-10-186665 discloses a photoresist composition comprising a copolymer having three kinds of repeating units of defined structures. Each of these copolymers comprises a repeating unit having one protolytically leaving group, by virtue of which it can be used as a resist material. However, even these copolymers have room for structural sophistication for magnifying the difference in the degree of change or for shortening the time necessary for the change to take place in characteristics, such as the solubility in alkaline aqueous solution, in the presence versus absence of a proton to thereby make them better suited for various applications.
In view of the above state of the art, the present invention has for its object to provide a protolytically leaving group-containing copolymer improved in characteristics such as solubility in alkaline aqueous solution in the presence of a proton, thus being applied for various purposes with advantage, and a production method of the copolymer.
The present invention relates to a protolytically leaving group-containing copolymer represented by the following general formula (1): 
in the formula, R1, R2 and R3 are the same or different and each represents a protolytically leaving group and a, b and c represent the amounts of existence (mole %) of repeating units (A), (B) and (C), respectively, in the copolymer,
which comprises the repeating unit (A) as well as the repeating unit (B) and/or the repeating unit (C) and
has a weight average molecular weight of 2000xcx9c30000,
said a, b and c satisfying the condition that a is 5 to 30 mole % and (b+c) is 70 to 95 mole %.
The inventors of the present invention explored into various protolytically leaving group-containing copolymers and, with attention first directed to the fact that the necessary copolymer structure is one comprising a repeating unit of the defined structure which comprises two protolytically leaving groups and a repeating unit of the defined structure which is adapted to provide hydrophilicity to the copolymer and/or a repeating unit of the defined structure which comprises one protolytically leaving group, found that by restricting the amounts of existence of said repeating units in the copolymer to defined ranges and, by restricting the weight average molecular weight of the copolymer to a defined range, the solubility of the copolymer in alkaline aqueous solution in the presence of a proton can be quickly increased to thereby provide a neat solution to the above problem. The present invention has been developed on the basis of the above finding.